Power

A student investigated the thermal conductivity of different metals.

Figure 2 shows some of the apparatus used.

Each rod was made from a different metal.

The metal rods are joined at the centre.

The size of each metal rod was the same.

This is the method used.

1. Attach a drawing pin to the end of each metal rod using wax.

2. Light the Bunsen burner.

3. Start a stopclock.

4. Record the time taken for the wax to melt and for the drawing pin to fall off each metal rod.

Table 1 shows the results.

Complete Figure 3.

You should:

• label the x-axis

• plot the data from Table 1 as a bar chart.

Which type of metal in Table 1 had the greatest thermal conductivity?

Give a reason for your answer.

Tick () one box.

The thermal energy transferred to the nickel rod was 132 J.

The temperature change of the rod was 20 °C.

mass of the nickel rod = 0.015 kg

Calculate the specific heat capacity of nickel.

Use the equation:

Use the Physics Equations Sheet to answer questions 02.4 and 02.5.

Write down the equation which links energy transferred (E), power (P) and time (t).

At the end of the investigation, the Bunsen burner was turned off.

As the nickel rod cooled to room temperature, the rod transferred 132 J of energy to the room.

The mean power transfer was 0.33 W.

Calculate the time taken for the energy transfer.

The process of nuclear fission is used in nuclear power stations.

Figure 17 shows the process of nuclear fission.

Complete the sentences.

Choose answers from the box.

In nuclear power stations, energy is released from

The uranium in Figure 17 splits into two parts and

The process of nuclear fission releases electromagnetic radiation in the

Use the Physics Equations Sheet to answer questions 10.2 and 10.3.

Write down the equation which links energy (E), power (P) and time (t).

A nuclear power station has a power output of 500 MW.

Calculate the energy output in 3600 s.

Give your answer in J.

Radioactive waste produced by nuclear power stations has a long half-life.

Suggest one precaution taken to reduce the hazard caused by radioactive waste from power stations.

Nuclear power stations do not generate electricity every day of the year.

One nuclear power station generated electricity for 92% of a year.

one year = 365 days

Calculate the number of days during the year that the nuclear power station generated electricity.

The process of nuclear fission is used in nuclear power stations.

Figure 2 shows the process of nuclear fission.

Complete the sentences.

Choose answers from the box.

In nuclear power stations, energy is released from

uranium.

The uranium in Figure 2 splits into two parts and

releases three.

The process of nuclear fission releases electromagnetic radiation in the

form of.

Use the Physics Equations Sheet to answer questions 02.2 and 02.3.

Write down the equation which links energy (E), power (P) and time (t).

A nuclear power station has a power output of 500 MW.

Calculate the energy output in 3600 s.

Give your answer in J.

Radioactive waste produced by nuclear power stations has a long half-life.

Suggest one precaution taken to reduce the hazard caused by radioactive waste from power stations.

Nuclear power stations do not generate electricity every day of the year.

One nuclear power station generated electricity for 92% of a year.

one year = 365 days

Calculate the number of days during the year that the nuclear power station generated electricity.

The UK uses renewable energy resources to generate some of its electricity.

Figure 4 shows the proportion of electricity generated by different renewable energy resources in the UK in 2020.

Calculate the percentage of electricity generated using hydroelectric power.

A remote village in the UK uses a hydroelectric generator to provide electricity.

The mass of water that passes through the hydroelectric generator each day is 2 500 000 kg.

The change in vertical height of the water is 15.0 m.

gravitational field strength = 9.8 N/kg

Calculate the decrease in gravitational potential energy of the water.

Use the equation:

gravitational potential energy = mass × gravitational field strength × height

Use the Physics Equations Sheet to answer questions 04.3 and 04.4.

Write down the equation which links energy (E), power (P) and time (t).

The hydroelectric generator transfers electrical power of 3000 W to the village.

Calculate the energy transferred to the village in 60 minutes.

The hydroelectric generator is turned by falling river water.

Figure 5 shows how the power output of the hydroelectric generator varied during one year.

Explain one reason why the power output varied.

A remote village in the UK uses a hydroelectric generator to provide electricity.

In one day, 2 500 000 kg of water passes through the hydroelectric generator. The change in gravitational potential energy of the water is 367.5 MJ. gravitational field strength = 9.8 N/kg Calculate the mean change in vertical height of the water as it moves through the hydroelectric generator. Use the Physics Equations Sheet.

The generator transfers 3.0 kW of electrical power. Calculate the time taken for the generator to transfer 2.16 × 10⁷ J of energy. Use the Physics Equations Sheet. Give your answer in standard form.

Figure 5 shows how the power output of the generator varied during one year.

A solar power system is installed in the remote village in addition to the hydroelectric generator. Explain why this improves the reliability of the electricity supply to the village. Use information from Figure 5.

A girl ran to the top of some stairs.

Figure 2 shows the stairs.

The girl measured the height of the stairs.

What measuring instrument should she have used?

The height of the stairs was 1.7 m.

The mass of the girl was 50 kg.

gravitational field strength = 9.8 N/kg

Calculate the change in gravitational potential energy of the girl.

Use the equation:

gravitational potential energy = mass gravitational field strength height

A boy ran up the same stairs and did 1800 J of work.

The time it took the boy to run up the stairs was 1.44 s.

Calculate the power of the boy.

Use the equation:

Which stop-clock was used to measure the time the boy took to run up the stairs?

Tick (✓) one box.

Stop-clock A
Stop-clock B
Stop-clock C

The boy had a speed of 2.0 m/s at the top of the stairs.

The mass of the boy was 70 kg.

Calculate the kinetic energy of the boy at the top of the stairs.

Use the equation: kinetic energy = 0.5 mass (speed)²

Figure 10 shows a girl doing an experiment to determine her power output by running to the top of some stairs.

The mass of the girl was 60.0 kg. The height of the stairs was 175 cm. The girl ran to the top of the stairs in 1.40 s. gravitational field strength = 9.8 N/kg Calculate the power output of the girl. Use the Physics Equations Sheet.

The total power output of the girl was greater than the answer to question 09.1. Suggest two reasons why.

A boy took more than 1.40 s to run up the same stairs. The power output of the boy was the same as the power output of the girl. What conclusion can be made about the boy’s mass?

Figure 13 shows an electric car being recharged.

The charging station applies a direct potential difference across the battery of the car.

What does ‘direct potential difference’ mean?

Which equation links energy transferred (E), power (P) and time (t)?

Tick (✓) one box.

The battery in the electric car can store 162 000 000 J of energy.

The charging station has a power output of 7200 W.

Calculate the time taken to fully recharge the battery from zero.

Which equation links current (I), potential difference (V) and resistance (R)?

Tick (✓) one box.

The potential difference across the battery is 480 V.

There is a current of 15 A in the circuit connecting the battery to the motor of the electric car.

Calculate the resistance of the motor.

Different charging systems use different electrical currents.

• Charging system A has a current of 13 A.

• Charging system B has a current of 26 A.

• The potential difference of both charging systems is 230 V.

How does the time taken to recharge a battery using charging system A compare with the time taken using charging system B ?

Tick (✓) one box.

Figure 1 shows an electric car being recharged.

The charging station applies a direct potential difference across the battery of the car. What does ‘direct potential difference’ mean?

Which equation links energy transferred (E), power (P) and time (t)? Tick (✓) one box.

The battery in the electric car can store 162 000 000 J of energy. The charging station has a power output of 7200 W. Calculate the time taken to fully recharge the battery from zero.

Which equation links current (I), potential difference (V) and resistance (R)?

Tick (✓) one box.

The potential difference across the battery is 480 V. There is a current of 15 A in the circuit connecting the battery to the motor of the electric car. Calculate the resistance of the motor.

Different charging systems use different electrical currents.

• Charging system A has a current of 13 A.

• Charging system B has a current of 26 A.

• The potential difference of both charging systems is 230 V.

How does the time taken to recharge a battery using charging system A compare with the time taken using charging system B ?

Tick (✓) one box.

During one year, 1.25 × 10¹⁸ J of energy was transferred from the National Grid. number of seconds in 1 year = 3.16 × 10⁷ Calculate the mean energy transferred from the National Grid each second. Give your answer to 3 significant figures.

Figure 5 shows a house with a solar power system. The solar cells generate electricity. When the electricity generated by the solar cells is not needed, the energy is stored in a large battery.

The charge flow through the cable between the solar cells and the battery in 24 hours was 27 000 coulombs. Calculate the mean current in the cable.

At one time, the total power input to the solar cells was 7.8 kW. The efficiency of the solar cells was 0.15 Calculate the useful power output of the solar cells.

It is unlikely that all of the electricity that the UK needs can be generated by solar power systems. Explain why.

Figure 14 shows a hydroelectric power station.

Electricity is generated when water from the reservoir flows through the turbines.

Write down the equation which links density (ρ), mass (m) and volume (V).

The reservoir stores 6 500 000 m³ of water.

Calculate the mass of water in the reservoir. Give your answer in standard form.

Write down the equation which links energy transferred (E), power (P) and time (t).

The electrical generators can provide 1.5 × 10⁹ W of power for a maximum of 5 hours. Calculate the maximum energy that can be transferred by the electrical generators.

Figure 15 shows how the UK demand for electricity increases and decreases during one day.

The hydroelectric power station in Figure 14 can provide 1.5 × 10⁹ W of power for a maximum of 5 hours. Give two reasons why this hydroelectric power station is not able to meet the increase in demand shown between 04:00 and 16:00 in Figure 15.

Figure 4 shows a hydroelectric power station.

Electricity is generated when water from the reservoir flows through the turbines.

Write down the equation which links density (ρ), mass (m) and volume (V).

The reservoir stores 6 500 000 m³ of water.

Calculate the mass of water in the reservoir. Give your answer in standard form.

Write down the equation which links energy transferred (E), power (P) and time (t).

The electrical generators can provide 1.5 × 10⁹ W of power for a maximum of 5 hours. Calculate the maximum energy that can be transferred by the electrical generators.

Figure 5 shows how the UK demand for electricity increases and decreases during

The hydroelectric power station in Figure 4 can provide 1.5 × 10⁹ W of power for a maximum of 5 hours. Give two reasons why this hydroelectric power station is not able to meet the increase in demand shown between 04:00 and 16:00 in Figure 5.

An electric kettle was switched on. Figure 10 shows how the temperature of the water inside the kettle changed.

When the kettle was switched on the temperature of the water did not immediately start to increase. Suggest one reason why.

The energy transferred to the water in 100 seconds was 155 000 J. specific heat capacity of water = 4200 J/kg °C Determine the mass of water in the kettle. Use Figure 10. Give your answer to 2 significant figures.

The straight section of the line in Figure 10 can be used to calculate the useful power output of the kettle. Explain how.

An electric car has a motor that is powered by a battery. A diesel car has an engine that is powered by diesel fuel.

Table 2 compares an electric car and a diesel car.

Give two advantages of the diesel car compared with the electric car in Table 2.

The mass of the battery in the electric car is 420 kg The total mass of the electric car is 1610 kg

Calculate the mass of the battery as a percentage of the total mass of the electric car.

Designers of electric car batteries want to increase the amount of energy that can be stored in a battery. Suggest two reasons why.

Figure 8 shows an electric car being recharged.

Write down the equation which links energy transferred, power and time.

The charger has a power output of 7000 W Calculate the time taken to transfer 420 000 J of energy to the car battery.

A scientist investigated how the maximum muscle power of humans varies with age and gender. The scientist asked volunteers to stand on a platform and to jump as high as they could. Figure 18 shows a volunteer taking part in the experiment.

An electronic timer measured the time that the volunteer was in the air.

The muscle power in watts per kg is calculated using the following equation:

One volunteer has a muscle power of 41 W/kg He was in the air for 0.12 s

Calculate his jump height.

Write down the equation which links kinetic energy, mass and speed.

One volunteer had a kinetic energy of 270 J and a speed of 3.0 m/s at the moment he left the ground. Calculate his mass.

Figure 19 shows the scientist’s results.

Compare the muscle power of males with the muscle power of females. Use data from Figure 19 in your answer.

The muscle power of each volunteer was measured five times. The highest muscle power reading was recorded instead of calculating an average. Suggest one reason why.

Light bulbs are labelled with a power input.

What does power input mean?

Tick (✓) one box.

Write down the equation which links current, potential difference and power.

A light bulb has a power input of 40 W

The mains potential difference is 230 V

Calculate the current in the light bulb.

Table 1 shows information about three different light bulbs.

Write down the equation which links efficiency, total power input and useful power output.

Calculate the value of X in Table 1.

In addition to power input, light bulbs should also be labelled with the rate at which they emit visible light.

Suggest why.

A scientist investigated how the maximum muscle power of humans varies with age and gender.

The scientist asked volunteers to stand on a platform and to jump as high as they could.

Figure 4 shows a volunteer taking part in the experiment.

An electronic timer measured the time that the volunteer was in the air.

The muscle power in watts per kg is calculated using the following equation:

One volunteer has a muscle power of 41 W/kg

He was in the air for 0.12 s

Calculate his jump height.

Write down the equation which links kinetic energy, mass and speed.

One volunteer had a kinetic energy of 270 J and a speed of 3.0 m/s at the moment he left the ground.

Calculate his mass.

Figure 5 shows the scientist’s results.

Compare the muscle power of males with the muscle power of females.

Use data from Figure 5 in your answer.

The muscle power of each volunteer was measured five times.

The highest muscle power reading was recorded instead of calculating an average.

Suggest one reason why.

Figure 7 shows a person using an electric lawn mower.

The lawn mower is connected to the mains electricity supply.

What is the frequency of the mains electricity supply in the UK?

The lawn mower has a switch on each side of the handle.

Figure 8 shows the circuit diagram for the lawn mower.

The motor in the lawn mower can only be turned on when the person using it holds the handle of the lawn mower with both hands.

Explain why.

The power input to the motor is 1.8 kW

The resistance of the motor is 32 Ω

Calculate the current in the motor.

The useful power output from the motor is 1.5 kW

Calculate the time it takes for the motor to transfer 450 000 J of useful energy.

Figure 14 shows a Bunsen burner heating some water in a beaker. Eventually the water changes into steam.

Explain how the internal energy of the water changes as it is heated from 20 °C to 25 °C

How is the particle model used to explain the difference in density between a liquid and a gas?

Tick (✓) one box.

A student measured the mass of boiling water that was turned into steam in five minutes.

Explain how the student could use this information to estimate the power output of the Bunsen burner in watts.

Nuclear power can be used to generate electricity through nuclear fission.

Figure 6 shows the process of nuclear fission.

Complete the sentences.

Choose answers from the box.

gamma rays light rays proton neutron nucleus X-rays

Electromagnetic radiation is released in the form of.

The UK needs at least 25 000 000 kW of electrical power at any time.

A nuclear power station has an electrical power output of 2 400 000 kW

Calculate how many nuclear power stations are needed to provide 25 000 000 kW of electrical power.

State two environmental issues caused by generating electricity using nuclear power stations.

The UK currently generates a lot of electricity by burning natural gas. This process releases carbon dioxide into the atmosphere.

Figure 7 shows how the concentration of carbon dioxide in the atmosphere has changed over the past 115 years.

Figure 8 shows how the global temperature has changed over the past 115 years.

Give one similarity and one difference between the data in Figure 7 and Figure 8.

Figure 10 shows a hot water tank made of copper.

Figure 10

Copper has a higher thermal conductivity than most metals.

How does the rate of energy transfer through copper compare with the rate of energy transfer through most metals?

Tick one box.

The tank is insulated. When the water is hot, the immersion heater switches off.

Complete the sentences.

Compared to a tank with no insulation, the rate of energy transfer from the

for longer.

Figure 11 shows how temperature varies with time for water in a tank heated with an immersion heater.

Figure 12 shows how temperature varies with time for water in a tank heated with a solar panel.

Figure 11

Figure 12

Give one advantage and one disadvantage of heating the water using solar panels rather than an immersion heater.

Use only information from Figure 11 and Figure 12.

Advantage of solar panels

Disadvantage of solar panels

During one morning, a total of 4 070 000 J of energy is transferred from the electric immersion heater.

4 030 000 J of energy are transferred to the water.

Calculate the proportion of the total energy transferred to the water.

Write down the equation that links energy transferred, power and time.

The power output of the immersion heater is 5000 W.

Calculate the time taken for the immersion heater to transfer 4 070 000 J of energy.

Give the unit.

Figure 13 shows a lift inside a building.

Figure 13

The motor in the lift does 120 000 J of work in 8.0 seconds.

Calculate the power output of the motor in the lift.

Use the equation:

The power input to the motor is greater than the power output.

Tick two reasons why.

Figure 14 shows part of the circuit that operates the lift motor.

Figure 14

The lift can be operated using either of the two switches.

Explain why.

Write down the equation that links gravitational field strength, gravitational potential energy, height and mass.

The lift goes up 14 m. The total mass of the people in the lift is 280 kg.

gravitational field strength = 9.8 N/kg

Calculate the increase in gravitational potential energy of the people in the lift.

Give your answer to 2 significant figures.

Figure 5 shows a cyclist riding along a straight, level road at a constant speed.

Complete the sentences.

in the cyclist’s body decreases.

The speed of the cyclist is constant when the work done by the cyclist is

Figure 6 shows how the speed changes as the power output of the cyclist changes.

Write down the equation that links power, time and work done.

Calculate the work done by the cyclist when his power output is 200 W for 1800 seconds.

Calculate the percentage increase in speed of the cyclist when the power output changes from 200 W to 300 W.

The maximum speed this cyclist can travel on a level road is 14 m/s.

How does cycling uphill affect the maximum speed of this cyclist?

Explain your answer.

Figure 16 shows a wind turbine.

Figure 16

At a particular wind speed, a volume of 2.3 ×10⁴ m³ of air passes the blades each second.

Calculate the mass of air passing the blades per second.

The power output of the turbine is directly proportional to the kinetic energy of the air passing the blades each second.

Describe the effect on the power output when the wind speed is halved.

At a different wind speed, the wind turbine has a power output of 388 kW.

The mass of air passing the wind turbine each second is 13 800 kg.

Calculate the speed of the air passing the blades each second.

Assume that the process is 100% efficient.